A process and a device of the aforesaid kind are known.
The German book "The control of gas exchange in high-speed internal combustion engines," by W. D. Bensinger, Springer-Verlag, 1968, describes, among other things, cam shapes in which the flanks, i.e. the connecting segments between the base circle and the secondary circle, do not have the usual convex shape, but rather a concave shape, which is also referred to as a "hollow flank" (German book page 31, FIG. 40c).
Cam shapes of this kind are used in engine design to achieve good combustion chamber filling characteristics by means of rapid valve actuation. Although it is also possible to achieve similar results by applying multiple-valve technology, multiple-valve technology is essentially effective only at high engine speeds, while a cam shape with hollow flanks also improves filling characteristics at low speeds.
With known processes and devices, however, the cams ground were always ones in which the radius of curvature in the concave curvature region (the hollow flank) was at least as great as the radius of curvature of the single grinding disk used. It was therefore possible, for geometrical reasons, to grind cams of this kind--i.e. first to rough down and then to finish grind them--without re-chucking and with one and the same grinding disk.
With known cams of this type, therefore, when concave curvature regions with a relatively small radius of curvature were desired, a correspondingly small grinding disk therefore needed to be used.
However, the use of small-diameter grinding disks very soon encounters practical limits if the entire cam machining process, i.e. both roughing and finish grinding, is to be performed with the same small grinding disk. Specifically, there arise thermal problems at the grinding disk surface, which are naturally greater in smaller-diameter grinding disks than in those with a large diameter. Furthermore, it is difficult to mount small-diameter grinding disks in a spindle in such a way that the required rotation speeds and drive power levels can be applied, since the grinding disk usually rotates about an axis that lies parallel to the camshaft axis. This then creates the danger, however, that the mounting system for the grinding disk will collide with adjacent cams on the same camshaft that are as yet unmachined or have already been machined, if the diameter of the spindle is as great as that of the grinding disk. Although the grinding disk could also, in a known manner, be allowed to rotate about an axis that is inclined with respect to the long axis of the camshaft, by giving the grinding disk a conical surface, this would nonetheless lead to geometrical errors, since with numerically controlled cam grinding using simultaneous rotation of the camshaft and movement of the grinding disk perpendicular to the camshaft (X axis), the engagement line between the grinding disk and the cam wanders in a direction perpendicular to the X axis.